netdev - Re: [PATCH 2/2] net/cdc_ncm: Increase NTB max RX/TX values to 64kb

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Date:   Mon, 4 Jul 2022 09:24:23 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Łukasz Spintzyk <lukasz.spintzyk@...aptics.com>
Cc:     netdev@...r.kernel.org, linux-usb@...r.kernel.org,
        oliver@...kum.org, kuba@...nel.org, ppd-posix@...aptics.com
Subject: Re: [PATCH 2/2] net/cdc_ncm: Increase NTB max RX/TX values to 64kb

On Mon, Jul 04, 2022 at 09:04:07AM +0200, Łukasz Spintzyk wrote:
> DisplayLink ethernet devices require NTB buffers larger then 32kb in order to run with highest performance.
> 
> Signed-off-by: Łukasz Spintzyk <lukasz.spintzyk@...aptics.com>
> ---
>  include/linux/usb/cdc_ncm.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/usb/cdc_ncm.h b/include/linux/usb/cdc_ncm.h
> index f7cb3ddce7fb..2d207cb4837d 100644
> --- a/include/linux/usb/cdc_ncm.h
> +++ b/include/linux/usb/cdc_ncm.h
> @@ -53,8 +53,8 @@
>  #define USB_CDC_NCM_NDP32_LENGTH_MIN		0x20
>  
>  /* Maximum NTB length */
> -#define	CDC_NCM_NTB_MAX_SIZE_TX			32768	/* bytes */
> -#define	CDC_NCM_NTB_MAX_SIZE_RX			32768	/* bytes */
> +#define	CDC_NCM_NTB_MAX_SIZE_TX			65536	/* bytes */
> +#define	CDC_NCM_NTB_MAX_SIZE_RX			65536	/* bytes */

Does this mess with the throughput of older devices that are not on
displaylink connections?

What devices did you test this on, and what is the actual performance
changes?  You offer no real information here at all, and large buffer
sizes does have other downsides, so determining how you tested this is
key.

Also, please wrap your changelogs at 72 columns like git asks you to do.

thanks,

greg k-h